1. Field of the Invention
The present invention relates to packages for semiconductor chips or other electronic devices.
2. Description of the Related Art
A typical package for a semiconductor chip includes an internal leadframe, which functions as a substrate for the package. The leadframe includes a central metal die pad and a plurality of leads that radiate outward from the die pad. A hardened, insulative encapsulant material covers the semiconductor chip (or die), die pad, and an inner portion of each of the leads. The semiconductor chip is mounted on the die pad and is electrically connected to the leads. In particular, the chip includes a plurality of bond pads, each of which is electrically connected by a bond wire or the like to a bond finger that is at an inner end of one of the leads. An outer portion of each lead extends outward from the encapsulant material, and serves as an input/output (I/O) terminal for the package. The outer portion of the leads may be bent into various configurations, such as a J lead configuration or a gull wing configuration.
Semiconductor chips that have a high degree of functionality, such as microprocessors, or that are used in high power applications, generate large amounts of heat. Accordingly, packages for such semiconductor chips must have the capacity to dissipate such heat to avoid a malfunction of the packaged chip.
A conventional heat dissipation solution in semiconductor packages includes the provision of a solid, machined copper or aluminum slug, which may or may not have fins, that is embedded in the encapsulant material of the package. Such a heat sink, however, has the drawback of a relatively low efficiency of heat dissipation even when fins are provided. Accordingly, an improved semiconductor package with a more efficient integrated heat sink is needed.
Embodiments of the present invention include semiconductor packages that have an active heat sink embedded in the package. The active heat sink is in a thermal connection with a semiconductor chip of the package. The encapsulant material of the package encapsulates the chip and a portion of the active heat sink. The chip is electrically connected to a plurality of external terminals of the package. The active heat sink includes a surface exposed to ambient and a cavity partially filled with a heat activated liquid. In some embodiments, an indirect thermal connection is provided between the heat activated liquid and a surface of the chip. Alternatively, a direct thermal connection can be provided between the heat activated liquid and a surface of the chip.
The heat activated liquid boils in response to heat generated during operation of the chip, thereby forming a vapor. The vapor condenses on a juxtaposed inner surface of the active heat sink and transfers heat to an opposite outer surface exposed to ambient to remove heat from the package. The inner and/or outer surfaces of the active heat sink can include fins to increase the surface areas of these surfaces. Optionally, an external heat sink including a plurality of fins can be thermally coupled to the outer surface that is exposed to ambient to further increase the surface area exposed to ambient.
By comparison to conventional heat dissipation solutions in semiconductor packages, the packages of the present invention provide much more efficient heat dissipation. This efficiency can be increased further through the use of fins, which may be included in or on the active heat sink and/or attached externally to the outer surface of the active heat sink that is exposed to ambient.
These and other aspects and features of the present invention will be better understood in new of the following detailed description of the exemplary embodiments and the drawings thereof.